The invention relates to a method of controlling a supervisory arrangement in a digital transmission system in which a plurality of repeaters are arranged between two terminal stations, a call message including an address number being transmitted by a terminal station towards the desired repeater. In addition, the invention relates to a supervisory arrangement for performing the method.
In digital transmission systems, repeaters must be used between two terminal stations. When bi-directional transmission between these terminal stations is used, these repeaters comprise a regenerator for the forward transmission and a regenerator for the return transmission. These regenerators serve, on the one hand, for pulse regeneration of the transmission signal and, on the other hand, for equalization of the transfer characteristic which in many cases is determined by a cable and is a function of the distance between two consecutive repeaters and of the ambient temperature.
In the terminal stations of the digital transmission system, supervisory arrangements are provided which check whether the digital transmission signals are disturbed, or not. After a disturbance has been detected, the individual repeaters, and consequently also the cable between these repeaters, are checked from a locating terminal station.
The European Patent Application No. 0,029,108 discloses such a supervisory arrangement. The method of controlling this arrangement is as follows. From a terminal station, a first switching pulse is conveyed to the first regenerator which causes the loop between the repeater for the forward transmission and the regenerator for the return transmission to be closed. Simultaneously, the first repeater conveys a signal to a second repeater, in response to which this second repeater is adjusted to a preparatory state. After the first repeater has been tested, the terminal station transmits a second switching pulse which causes the loop closure of the first repeater to be eliminated and the loop between the regenerator for the forward transmission and the regenerator for the return transmission in the second repeater to be closed. The second repeater supplies a signal which adjusts the third repeater to a preparatory state. In similar manner each subsequent switching pulse effects in a subsequent repeater loop closure between the regenerators for the forward and the return transmissions, while the next repeater is adjusted to a preparatory state.
The method of controlling the prior art supervisory arrangement has the disadvantage that the link must be put out of service during testing of the repeaters. A further disadvantage is that the repeaters can only be tested sequentially. So separate, random testing of individual repeaters is not possible. In addition, the position of a repeater is determined from the number of switching pulses transmitted by the terminal station. There is, however, no possibility to check whether this method of location operates correctly, so that incorrect conclusions may be drawn as regards the location of defective repeaters.